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<br />Memo to Erica Crosbv 4 March 22 2000 <br />discussed above, should not be released until the Division of Minerals and Geology and the Office of <br />the State Engineer are satisfied that the specified leakage criteria has been met. <br />As stated above, it is pertinent to the bond amount that the depth to bedrock used in estimating the <br />extent of the slurry wall required is accurately determined and that nature of the bedrock is investigated. <br />The applicant should provide information from boreholes at the site showing the depth to gravel and the <br />type of bedrock present, any variability in the bedrock encountered, and the depth of weathering in the <br />bedrock. It is implicit to the proposed slurry wall plan that the bedrock is a competent seepage barrier, <br />and this is most likely to be the case. However, if fractured zones, sandy lenses or layers, or deeply <br />weathered bedrock are present, pit floor lining or a deeper bedrock keyway for the slurry wall may be <br />required. Either solution would increase the reclamation costs that may be imposed upon the State in a <br />bond forfeiture and must be covered by the bond. Assuming that the borehole information <br />demonstrates that the bedrock is no more than 36 feet below the surface and is an adequate seepage <br />barrier, [he following estimate is provided for the Ft. Lupton Sand and Gravel Mine Slurry Wall. <br />36'depth x 8222' length x $3.00/sq.ft. _ $887,976.00 direct costs <br />If the 20% regulated construction bond is selected the required bond for slurry wall installation <br />would be $177,595.00. <br />These estimates are substantially more than the $96,664.00 estimated by the applicant in Exhibit L. It <br />appears that in the applicant's estimate inadvertently applies a unit cost per sq. ft. to a volume in cubic <br />yards. <br />Reeulatory Resposibilities <br />The applicant states that the final approval and success criteria for the performance of the slurry wall to <br />seal and isolate the reservoir-storage from the surrounding alluvial aquifer lies with the State Engineer, <br />which is of course true. In fact, the most straightforward mechanism for release of a slurry wall bond is <br />for an Operator [o demonstrate and document compliance with the Stale Engineer's lined reservoir <br />performance standards. However, the Division of Minerals and Geology is required to hold financial <br />warranties sufficient to assure [hat the State Engineer's standards will be met. A copy of the <br />Memorandum of Understanding between the Division of Minerals and Geology and the Office of the <br />State Engineer is attached and describes the division of responsibilities between the two agencies. <br />Interior Dike <br />The applicant states that the proposed interior dike will be oriented pazallel to potential flood flows and <br />will be at a low, 3 foot, profile above the high water level of the reservoir. The dike will also employ a <br />cross drain between the two reservoirs, and [he applicant will be providing written agreements with <br />owners of structures to be relocated onto [he dike. All of these factors tend to mitigate any concern <br />with the stability of the backfill. However, Rule 3.1.5 requires an applicant to describe how backfilled <br />